The Kyshtym accident: causes, scale and radiation characteristics

The Kyshtym accident took place on 29 September 1957 at a plutonium separation plant. The accident was caused by the explosion of dry nitrate and acetate salts in a tank containing highly radioactive wastes as a result of a failure in the cooling system and the consequent self-heating of the wastes. The explosion dispersed approximately 2 million curies of nuclear fission products, of which 144Ce and 95Zr accounted for 91%. Long-lived 90Sr accounted for only 2.7% of the dispersed mixture but was responsible for the long-term radiological hazard within what became known as the Eastern Urals radioactive trail. An area of 300 x 5O km received a minimum contamination level of 0.1 Ci of 90Sr/km2, and an area 105 x 9 km a minimum level of 2 Ci 90Sr/km2. The spatial distribution of the contamination was fairly typical of models of single-point discharge and dry atmospheric deposition of contaminants; the result was a sharply defined trail axis and a steady falling-off of contamination level both along and across the axis. The maximum contamination was 4 000 Ci of 90Sr/km2. The initial exposure dose rate reached 150 μR/h per 1 Ci of 90Sr/km2 and was mainly due to 95Zr and 95Nb. The exposure dose over 30 years was 0.5 R/(Ci 90Sr/km2), of which 0.42 R/(Ci 90Sr/km2) was formed during the first year. As a result of radioactive decay, contamination by all radionuclides decreased over 30 years by more than 30 times, and fell by half in the case of 90Sr, while the exposure dose rate decreased by 2 800 times and radionuclide concentration in the various parts of the environment by 103-104 times. All the short-lived radionuclides decayed within the first five years, after which time 90Sr was practically the only factor determining the radiation and radiological characteristics of the Eastern Urals radioactive trail. The processes governing 90Sr migration in the environment and in human food chains determine the radiological consequences of the accident for human beings. (author)